It is a conventional practice to employ plasticizers in polyvinylchloride insulation materials such as are commonly used to provide insulation over electrical wiring. Plasticizers are used both as processing aids during handling of the polyvinylchloride resin formulation and its extrusion on to the electrical wire and also as end use modifiers where they affect the chemical and/or physical characteristics of the insulation on the final electrical product.
While many types of plasticizers are used in polyvinylchloride insulation covering on electrical wires and cables, the most widely employed are polybasic aromatic acid esters. These plasticizers are the reaction products of aliphatic alcohols with polybasic aromatic acids, principally phthalic acid and trimellitic acid.
The most widely used polybasic aromatic acid esters are dialkyl phthalates, examples of which include di-2-ethylhexyl phthalate (DOP), di-isooctyl phthalate (DIOP), di-isodecyl phthalate (DIDP), di-N-octyl N-decyl phthalate (DNODP), di-N-decyl phthalate (DNDP) di-undecyl phthalate (DUP) and di-tridecyl phthalate (DTDP). The aforementioned phthalatic acid based plasticizers are conventionally used in low to moderate temperature applications. However, in high temperature wiring applications, e.g., 90.degree. C. and 105.degree. C. wiring, it is a conventional practice to use plasticizer systems composed of substantial amounts of trimellitate esters. The trimellitate esters are considered to be more stable to oxidation loss from the polyvinylchloride resin formulation and thus more suitable for use in high temperature environments. Trimellitate acid based plasticizers include trioctyl trimellitate (TOTM) triisooctyl trimellitate (TIOTM), N-octyl, N-decyl trimellitate and triisononyl trimellitate (TINTM).
In addition to containing plasticizers, polyvinylchloride insulations will also normally contain stabilizers to retard degradation of the PVC during processing and during use, antioxidants and fillers. The stabilizers may be either organic, or inorganic, or combinations of both. The antioxidants are added in order to prevent oxidative degradation of the plasticizer and also the polyvinylchloride resin. The antioxidants normally employed in formulating PVC insulation are sterically hindered phenols. Bisphenol A (BPA) is the most widely used. Bisphenol A is employed in PVC formulations in only very small amounts, usually substantially less than one weight percent based on the amount of plasticizer in the formulation.